Preparation of Ag-Ni-Cu Composite Material by Ultrasonic Arc Spray Forming and Accumulative Roll Bonding and the Evoluti
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ALLOYS of the Ag-Ni system are used widely as electrical contact materials in electrical devices.[1–12] Until now, these immiscible Ag-Ni alloys, which exhibit high melting points, have been manufactured by conventional powder metallurgy processes such as chemical coprecipitation and mechanical mixing. However, both of these processes are complex and costly. In addition, in the resulting alloys, Ni and Ag exist in the form of a single mixture. This has significant effects on the properties of the electrical contact materials. A few characteristics that help improve the performance of electrical contact materials based on Ag-Ni-Cu alloys are having a uniform structure, ensuring that Ni exhibits supersaturated solid solubility in the a-Ag phase, and having a fine-grained a-Ag phase. In order to shorten the duration of the production process and to improve the performance of the Ag-Ni alloys, these alloys have been synthesized from Ag-Ni composite powders using traditional water atomization and gas atomization techniques.[3–5] However, because the melting points of the crucible and nozzle are low, they are easily damaged and can contaminate the produced alloy samples. In addition, the Ni content of the coarse powder used as the starting material is less
KE ZHANG, Senior Engineer, is with the College of Physical Science and Technology, Yunnan University, No 2 Green Lake Road, Kunming 650091, P.R. China, and also with the Northwest Institute for Nonferrous Metal Research, No 96 Weiyang Road, Xi’an 710016, P.R. China. GUO-YI QIN, Senior Researcher, SI-YONG XU and JIN-XIN GUO, Senior Engineers, are with the College of Physical Science and Technology, Yunnan University. Contact e-mail: [email protected] GUANG MA, Senior Researcher, is with the Northwest Institute for Nonferrous Metal Research. Manuscript submitted October 16, 2013. METALLURGICAL AND MATERIALS TRANSACTIONS A
than or equal to 5 wt pct. Using mechanical alloying to obtain a larger solid solution and high-dispersion a-Ag and b-Ni composite powders, the performance of the resulting materials can be improved.[13–15] However, given the length of the mechanical alloying process as well as its low efficiency and high cost, it has little practical application. Ultrasonic arc spray forming (UASF) is a new type of net-shape rapid solidification technology for fabricating composite materials. It can be described as follows. Two metal or alloy wires, used as the positive and negative electrodes, are fed into the UASF system by an automatic wire feeder. The electrodes are then melted by the high temperature of the arc between the positive and negative electrodes, resulting in metal droplets. These metal droplets are atomized into finer droplets by an ultrasonic jet flowing through a Laval nozzle. Finally, the fine droplets are ejected by rotation (or another type of movement) and deposited on a substrate, forming excellent semifinished products, and workpieces. The UASF technique is a relatively new method and was proposed by Qin et al.[9] in 2006. The microstructures
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